1. Field of the Invention
The present invention relates to an apparatus for magnetically recording and/or reproducing a digital signal, such as, the PCM audio signal of a so-called 8-mm video tape recorder (VTR) or the like.
2. Description of the Prior Art
In the 8-mm VTR, the audio signal is digitally recorded and reproduced in the form of a pulse code modulated (PCM) signal in a portion of each of the slant tracks on a magnetic recording tape, for example, as described in further detail in U.S. Pat. No. 4,551,771, having a common assignee herewith. In such recording of the PCM audio signal by an 8-mm VTR, as standardized, the audio signal is sampled at a frequency about twice the horizontal frequency of the video signal being recorded in the remaining portion of each slant track, for example, with a sampling frequency of 31.5 kHz in the case of the NTSC standard, and is encoded in polygonal-line 8 bits (corresponding to rectilinear 10 bits) prior to being recorded in accordance with the so-called bi-phase system. In the bi-phase system, each bit which is a binary "1" is represented by a first frequency, and a second or different frequency represents each bit which is a binary "0".
Further, for the recording and reproducing of video signals, it has been proposed to employ a high coercive magnetic substance as the recording medium so as to extend the transmission bandwidth and thereby provide a video image of relatively higher quality. In such case, the combination of the extended transmission bandwidth and the use of the 8-10 modulation or conversion system employed in the so-called R-DAT or the like, for example, as disclosed in U. S. Pat. Nos. 4,577,180 and 4,617,552, also having a common assignee herewith, enables the PCM audio recording to greatly improve the quality of the recorded sound by permitting the sampling of the audio signal at a relatively high sampling frequency, for example, at 48 kHz, and by encoding the same in rectilinear 16 bits.
The modulation/demodulation circuits or modem required for the recording and reproducing of the PCM audio signal in accordance with bi-phase system or mode are substantially different, in format, from the modulation/demodulation or modem required for recording and reproducing of the PCM audio signal in accordance with the more recently proposed or developed 8-10 modulation or conversion system or mode. Accordingly, in an apparatus provided for reproducing the PCM audio signal recorded in accordance with either the bi-phase system or mode or the 8-10 modulation system or mode, it is necessary to employ first and second signal processing circuits adapted to the formats of the bi-phase system or mode and the 8-10 modulation system or mode, respectively, and further to detect the format of the signal being reproduced and enable operation of the respective one of the signal processing circuits. However, in the prior art, there has not been developed an appropriate method or apparatus for discriminating between the different formats with which the PCM audio signal may be recorded.
In the case of the R-DAT, it is possible to record in a selected one of a plurality of modes employing different sampling frequencies of, for example, 48 kHz, 44.1 kHz and so on. However, these various modes in the R-DAT employ the same recording format for the modulating system so that the several modes can be identified or discriminated by means of respective ID codes included in the digital signal to be recorded. In a reproducing operation, the ID code included in the recorded digital signal is readily detected for controlling the change-over or selection of the signal processing circuits. On the other hand, since the formats for the modulation system or the like are quite different for the bi-phase system and for the 8-10 modulation or conversion system, it is not possible to use an ID code included in the digital signal for controlling the selection of the signal processing circuits.